After retrieving the mastermind behind the Immune communications network, Nathan James finds itself trapped between the sub and civilian blockades set up by the Immunes. Chandler sends Dr. Scott and the cure off the ship under the protection of XO Slattery as the James heads towards its inevitable final showdown with the sub.

With a small group of survivors from Solace in tow, Chandler and his crew square off against an enemy of the most dangerous kind – a nuclear-powered submarine led by rogue British naval officers, Sean and Ned Ramsey. XO Slattery interrogates a captured mercenary from the hospital ship in an effort to extract information on the sub and its mission. As Nathan James engages in a perilous game of cat-and- mouse, the truth about the mercenary sub unfolds.